This invention relates generally to a bolster bearing or liner disposed between the bolster bowl of a truck bolster and the center plate of a car body bolster, and more particularly to a cup-shaped bearing engaged with the truck bolster against rotation in a first position as well as in a second position radially shifted relative thereto.
As is well known the center plate of a rail car body has a cylindrical boss which mates with a cylindrical socket forming a bolster bowl in the truck bolster which forms part of the car body underframe. A king pin extends through centrally aligned openings in the body bolster, center plate and bolster bowl about which the truck bolster may rotate relative to the car body. The cast bolster bowls are known to rapidly wear since the weight of the car body is transmitted to the truck bolster via the center plate and mating bolster bowl thereby developing considerable friction at such engaged surfaces. The center plate will likewise become worn in service and must therefore be periodically replaced. Although replacement of the center plate is relatively easy excessive wear of the bolster bowl rendering the truck bolster unserviceable requires a complete diassembly of the car truck for replacement.
Hardened steel liners are typically inserted between the mating surfaces of the center plate and bolster bowl for minimizing the aforedescribed wear problems. These liners normally include a circular plate fitted into the bottom of the bowl and an annular wear ring extending around the side of the bowl. The wear ring is normally secured in place to the truck bolster by means of a joint weld between the ring and the rim of the bolster bowl. However, due to extremely rough handling during the service life of the rail car and because of the inherently weak welds developed in joining different steels together, i.e., the wear ring, usually of manganese steel, with the bolster bowl, usually a cast mild steel, the weld joints crack and fail to properly retain the ring in place. Moreover, by the very nature of manganese steel material, the wearing undergoes grain growth (creep) while being work-hardened in service, likewise causing the welds to develop incipient cracks, leading to ultimate failure.
An attempt in avoiding the problem of securely retaining a hardened liner in a bolster bowl of a rail car truck bolster is disclosed in U.S. Pat. No. 3,713,710 wherein a retainer plate overlaps the wear ring and is welded to only the truck bolster. Such retainer plate is formed of a steel which is, from a welding standpoint, compatible with the steel from which the truck bolster is formed so as to hopefully avoid weld locations subjected to high stress concentrations when the rail car experiences severe impacts, and to likewise avoid the problem of weak welds when joining two different steels. The wear ring is alternatively held in place by a tongue and groove arrangement, by a press fit arrangement, or by welding the ring at opposite ends to the rim of the bolster bowl and to the bottom wear plate.
Such prior art arrangements nevertheless fail to effectively avoid the problems caused by weakened weld joints especially when the hardened steel liner undergoes creep while being work-hardened in service. And, in the prior art arrangement whereby the wear ring and wear plate are interconnected by welding and the wear ring is welded to the bolster bowl rim, failure of the weld joint between the ring and rim may allow relative rotation between the wear plate and the bolster bowl thereby causing excessive bolster bowl wear and bringing about the need for costly and tedious replacement thereof.
Another problem not solved by the prior art arrangements concerns that of uneven wear of the liner in a longitudinal or in a transverse direction relative to car movement. It would be advantageous to rotate the liners through 90.degree. so as to expose unworn surfaces thereof to the center plate depending on whether the principle wear of the liners occurs longitudinally or transversely. However, because the prior art wear liners are welded in place to the truck bolster, they are obviously incapable of being rotated for such purpose.